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Unit 2 Heroes Ⅰ.阅读理解 A LOS ANGELES—Old people who keep walking a relatively long distance may be less likely to suffer from cognitive(认知的) decline，a new study suggests. “By walking regularly，and maintaining a little bit of moderate physical activity，you can reduce your likelihood of developing Alzheimer's disease and spare brain tissue，” Kirk I．Erickson，the study's lead author，said. Erickson and his colleagues from the University of Pittsburgh began to establish a link between walking and memory in 1989. According to the report on their study published online Wednesday in Neurology，an official journal of the American Academy of Neurology，researchers tracked the physical activity and cognitive patterns of nearly 300 adults. At the very beginning，all participants，on average 78 years old and about two－thirds being women，were in good cognitive health.The researchers charted how many blocks each person walked in one week. Nine years later，the participants were given a MRI scan to measure their brain size.All of them were deemed to be“cognitively normal.” But after four more years，test showed a little more than one third of the participants had developed a mild cognitive impairment or dementia. By correlating cognitive health，brain scans and walking patterns，the research team found that being more physically active appeared to lower the risk of developing cognitive impairment. | 
